These days, a radio communication system, such as portable telephone system and radio LAN (Local Area Network), is widely used. In the field of radio communication, continuous discussions as to next-generation communication technologies is made in order to further improve communication speed and communication capacity. As the next-generation communication technology, for example, standardization regarding LTE and LTE-Advanced is completed or is under consideration.
With regards to LTE and LTE-Advanced, OFDM (Orthogonal Frequency Division Multiplexing; orthogonal frequency division multiplexing) scheme is adopted as a modulation scheme of downlink communication from a base station apparatus to a mobile station apparatus. The OFDM scheme, for example, is a communication scheme in which a frequency bandwidth is divided into a plurality of bandwidths or subcarriers, and information data is mapped on respective frequency bandwidth orthogonal to each other.
In contrast, SC-FDMA (Single Carrier-Frequency Division Multiple Access: single carrier-frequency division multiple access) scheme is adopted as a modulation scheme of uplink communication from the mobile station apparatus to the base station apparatus. The SC-FDMA, for example, is a communication scheme in which a frequency bandwidth is divided, and data is transmitted with the use of a different frequency bandwidth between a plurality of mobile station apparatuses. The SC-FDMA scheme is a single carrier transmission, compared with the OFDM scheme, so that PAPR (Peak to Averaged Power Ratio: peak to average power ratio) can be reduced. Accordingly, the SC-FDMA scheme can reduce the power consumption of an amplifier and reduce the whole power consumption of the mobile station apparatus, compared with OFDM scheme.
In the SC-OFDM scheme, for example, waveform equalization processing is performed in the base station apparatus on the reception side, so that propagation distortion in a radio channel can be suppressed. Then, the mobile station apparatus periodically inserts CP (Cyclic Prefix) into a transmission signal, which makes it possible to perform the waveform equalization processing in a frequency domain in the base station apparatus. An arithmetic processing amount in the frequency domain in the base station apparatus can be reduced by the insertion of CP, compared with an arithmetic processing amount in a time domain. However, for example, when a timing difference between reception signals is larger than a CP length, orthogonality between the reception signals is not maintained, and interference between the signals occurs, and reception quality deteriorates, compared with a case where the timing difference between the reception signals falls within the CP length. Accordingly, in the base station apparatus, transmission timing control is performed with respect to each mobile station apparatus, in order to prevent a timing discrepancy between the reception signals.
FIG. 23 is a flowchart illustrating the example of operation of the transmission timing control. A mobile station apparatus UE (User Equipment) transmits a data signal or a pilot signal (Sounding Reference Signal: SRS) to a base station apparatus eNB (evolved Node B) (S110). The base station apparatus eNB measures a timing difference between a transmission frame and a reception frame regarding the data signal (S111), obtains a timing correction amount NTA based on a measured value, and feeds back the timing correction amount NTA as a control signal (S112).
FIG. 24 is a diagram illustrating an example of a difference between a frame timing (downlink transmission timing) of the base station apparatus eNB and a frame timing (uplink transmission timing) of the mobile station apparatus UE. The mobile station apparatus UE which receives the control signal from the base station apparatus eNB transmits the data signal earlier by a time interval obtained by adding a fixed value NTAoffset to the timing correction amount NTA and multiplying a fixed value Ts than the frame timing that the mobile station apparatus UE grasps. Accordingly, the base station apparatus eNB can receive the data signal transmitted from the mobile station apparatus UE at a timing in synchronism with the frame timing.    Non-Patent Document 1: 3GPPTS 36. 211 V9. 1. 0    Non-Patent Document 2: 3GPPTS 36. 212 V9. 1. 0    Non-Patent Document 3: 3GPPTS 36. 213 V9. 1. 0    Non-Patent Document 4: 3GPPTR 36. 913    Non-Patent Document 5: 3GPPTR 36. 814
However, a plurality of mobile station apparatuses UE include a different discrepancy in uplink transmission timing, so that the uplink transmission timing control described above is performed for each mobile station apparatus UE. Accordingly, when the base station apparatus eNB connects to a plurality of mobile station apparatuses UE and performs the transmission timing control in a cell, the base station apparatus eNB feeds back the control signal including the timing correction amount NTA to the plurality of mobile station apparatuses UE. For this reason, the transmission amount of the control signals transmitted from the base station apparatus eNB is increased corresponding to an increase in the number of mobile station apparatuses UE, and accordingly, overhead regarding the transmission of the control signals is increased.
FIG. 25 is a diagram illustrating an example of the transmission timing control with respect to the plurality of mobile station apparatuses UE in a running train. In this case, the base station apparatus eNB performs the transmission timing control with respect to the respective plurality of mobile station apparatuses UE in accordance with the movement of the train. Similarly, the base station apparatus eNB feeds back the control signals corresponding to the number of the plurality of mobile station apparatuses UE and performs the transmission timing control. Accordingly, the overhead of the control signal transmitted from the base station apparatus eNB is increased corresponding to an increase in the number of mobile station apparatuses UE.